SpamAssassin examines your mail using numerous heuristic filters and assigns a spam score based on matches it finds. Citadel can attach directly to SpamAssassin without the need to install or configure any filters.

You should configure SpamAssassin to reject messages with attachments that are Windows executables, because these are almost always malware. If users complain, suggest archive formats such as Zip. Free and easy to use zip tools are commonly available. Save yourself and your users work.

You can also configure SpamAssassin to outrightly reject (by scoring extremely high) any message which contains a URL whose hostname resolves to an IP address on one of the various blacklists. These tests are disabled by default! You have to enable and high-score them by putting the following lines into SA local.cf:

Citadel's SpamAssassin integration only works on a site-wide basis. Spam is bounced; ham (non-spam) is delivered. If you wish to change this behavior you can reconfigure Citadel to only flag spam instead of rejecting it. In this case, each user will need to have a spam handling rule on their inbox. In this case, each user can choose to either reject or quarantine incoming spam.